1. Field of the Invention
The present invention relates to a chemically amplified resist material and a patterning method that uses the same. More particularly, the present invention relates to a chemically amplified resist material useful for forming patterns for microfabrication in the production of semiconductor devices and magnetic heads, and a patterning method that uses the chemically amplified resist material.
2. Description of the Related Art
In recent years, chemically amplified resists containing photo acid generators have been widely used for microfabrication of semiconductor devices (see, for example, J. M. J. Frechet, et al., Proc. Microcircuit Eng., 260 (1982); H. Ito, et al., “Polymers in Electronics”, ACS Symposium Series 242, T. Davidson., ed., ACS, 11 (1984); and, U.S. Pat. No. 4,491,628 (1985)). Chemically amplified resists generate acids from photo acid generators by being irradiated with ultraviolet rays, electron beam, X-rays or convergent ion beam, and this acid functions as a catalyst during post exposure bake, with the resulting catalytic reaction changing the exposed portion into alkaline-soluble (in the case of a positive resist) or alkaline-insoluble (in the case of a negative resist). Consequently, the use of a chemically amplified resist makes it possible to improve exposure sensitivity.
As chemically amplified resists use a catalytic reaction driven by an extremely small amount of acid, they are susceptible to the effects of external impurities. If the impurities are basic species in particular, they are known to cause deactivation of the acid that leads to deterioration of the form of the pattern formed by exposure and development. Those locations at which deterioration of the pattern form occurs are in close proximity to the interface between the upper and lower portions of the formed pattern (surface layer and bottom of the resist film), and this deterioration is mainly caused by basic species present in the atmosphere and on the substrate surface, respectively.
With respect to the effect of basic species present in the atmosphere, since basic species adsorbed onto the surface layer of the resist film and basic species diffused in the resist film from the surface layer neutralize an acid generated from the photo acid generator by exposure, solubilization (in the case of a positive resist) or insolubilization (in the case of a negative resist) of the resist material near the surface layer of the resist film of the exposed portion is impaired. As a result, the pattern of a positive resist takes on the shape of a T-top (formation of a poorly dissolving surface layer), while the pattern of a negative resist takes on the shape of a round top (missing upper portion of the pattern).
On the other hand, with respect to the effects of basic species from the substrate, since basic species present on the substrate surface and basic species diffused in the resist from the substrate surface neutralize the acid generated by exposure, solubilization (in the case of a positive resist) or insolubilization (in the case of a negative resist) of the resist material near the interface with the substrate is impaired. As a result, the pattern of a positive resist takes on the form of a footing, while the pattern of a negative resist takes on the form of an undercut. The effects of basic species from the undercoating in this manner are even more remarkable in cases in which a film containing basic species such as SiN, SiON, TiN, BPSG, BSG or PSG is formed on the substrate surface. In addition, footings and undercuts similarly occur due to diffusion of acid generated in the resist into an underlying film.
The occurrence of pattern defects such as the T-top, round top, footing or undercut as described above prevents the underlying film from being processed to the predetermined dimensions, thereby making microfabrication of semiconductor devices difficult.
Although the effects of basic species in the atmosphere can be suppressed to a certain extent by controlling the process atmosphere by, for example, using a basic species adsorbing filter, this results in the problem of excessive complexity of the production equipment.
On the other hand, the formation of a protective film comprised of a thermosetting resin and so forth between the substrate and resist film had been proposed as a method for avoiding the effects of basic species from the substrate. However, the protective film must be coated to an adequate thickness by a method such as spin coating or CVD and so forth in order to suppress diffusion of the basic species. In addition, there are cases when the removal of this protective film following patterning of the resist film requires an etching agent that differs from the developing solution of the resist, thereby resulting in the problem of causing the process to become excessively complex.